I'll try and keep this short.
The big benefits of Chromebooks are low cost, low maintennce, limited software, and built to thing everyone does; get online.
In education the devices are a boon because of these factors and of the fact Chromebooks come with Google Apps schools don't have to pay extra for. All this will be a challenge for Windows Cloud.
Now it's not an unwinnable fight.
For one the Chromebook growth seems to be limited as of now. North America and especially the US is where they've seen movement. Also those Chrome OS gains come at the expense of Macs/iOS. Secondly Chrome is still reliant (or seems to be heavily reliant on) a web connection. This is fine for places where there is a steady internet, but not everywhere.
For Windows Cloud Microsoft could make the argument about creating a platform that 1) grows with the student, 2) Offers software/services that enhance learning, and 3) Is low maintence for teachers and staff.
Now for Microsoft the key will be in balancing the heaviness of Windows with its benefits. Chrome is light and fast and limited. And by liited I mean their is enough there to get things done, but not enough for distraction. Windows will have to match that. In Redmond's favor Cloud offers offline in ways ChromeOS doesn't.
Also Microsoft is going to have to over FREE apps. I mean OneNote is a big thing for Cloud but they need the full Office suite there. I mean this is anecdotal but a lot of students grabbed RT devices because they were simple, good enough Word devices.
Lastly Microsoft needs to stick the landing with mangeability. Chromebboks don't require an IT staff and Windows Cloud shouldn't either. This might be the biggest hurdle for Microsoft. We will see how it goes on May 2.